Sign up to receive free email alerts when patent applications with chosen keywords are publishedSIGN UP

Abstract:

A modular and scalable high-power fiber laser system is configurable to
generate 1 kW or more of laser output, and includes one or more separable
pump modules separately disposed from each other, each pump module
including a plurality of fiber-coupled component pump sources optically
combined by one or more fiber-based pump module pump combiners, each pump
module providing one or more pump module fiber outputs, and a gain module
separately disposed from the one or more separable pump modules and
including one or more gain module pump fiber inputs optically coupled to
corresponding ones of the pump module fiber outputs, and including a gain
fiber optically coupled to the one or more gain module pump fiber inputs,
the gain fiber configured to generate a gain module fiber output power
scalable in relation to the number and power of said pump module fiber
outputs coupled to the gain fiber.

Claims:

1. A modular and scalable high-power fiber laser system configurable to
generate 1 kW or more of laser output, comprising: one or more separable
pump modules separately disposed from each other, each pump module
including a plurality of fiber-coupled component pump sources optically
combined by one or more fiber-based pump module pump combiners, each pump
module providing one or more pump module fiber outputs; and a gain module
separately disposed from said one or more separable pump modules and
including one or more gain module pump fiber inputs optically coupled to
corresponding ones of said pump module fiber outputs, and including a
gain fiber optically coupled to said one or more gain module pump fiber
inputs, said gain fiber configured to generate a gain module fiber output
power scalable in relation to the number and power of said pump module
fiber outputs coupled to said gain fiber; wherein a path from each of
said pump sources to the output of said gain module is all-fiber.

2. The system of claim 1, wherein said one or more gain module pump fiber
inputs are optically coupled to said corresponding pump module fiber
outputs at serviceable splice locations.

3. The system of claim 1, wherein said gain module includes one or more
combiners of the pump or pump-signal type, said combiners configured to
optically couple said one or more gain module pump fiber inputs to said
gain fiber.

4. The system of claim 1, wherein said gain fiber is incorporated into a
master fiber oscillator and fiber amplifier.

5. The system of claim 4, wherein said fiber amplifier includes two or
more gain stages.

6. The system of claim 1, wherein said gain fiber is incorporated into a
fiber oscillator.

7. The system of claim 1, wherein said gain fiber is pumped in one or
more ways selected from the group consisting of co-pumping,
counter-pumping, end-pumping, side-pumping, and bi-directionally pumping.

8. The system of claim 3, wherein said one or more gain module pump fiber
inputs are coupled to an input of said combiner at a central location
concentric with a central axis thereof and at one or more locations
radially offset from said central axis.

9. The system of claim 8, wherein an aiming beam is coupled into an
aiming fiber coupled to said gain module pump fiber input coupled to said
central location.

10. The system of claim 8, wherein said gain module pump fiber input
coupled to said central location provides a beam dump output for
backward-propagating light in said gain fiber.

11. The system of claim 3, wherein at least two of said gain module pump
fiber inputs are unused and paired off via splicing.

12. The system of claim 1, wherein said gain module output provides an
output beam of about 1 kW or greater.

13. The system of claim 1, wherein said pump sources are fiber-coupled
laser diode modules, each including a plurality of single-emitter diode
lasers, the diode laser beams of which are collimated, combined, and
focused into a pump source optical fiber.

14. The system of claim 1, further comprising a cooling system coupled to
said gain module and said one or more pump modules such that each module
is thermally isolated from each other module.

15. (canceled)

16. The system of claim 1, wherein said gain module includes a signal
combiner configured to receive a plurality of signal beams produced in
said gain module and to combine the signal beams to form a high-power
output of the fiber laser system.

17. The system of claim 1 further comprising at least another said gain
module.

18. The system of claim 1 wherein said pump module fiber outputs are
optically coupled to said gain module pump fiber inputs with pluggable
connectors.

19. A high-power fiber laser system, comprising: a gain module configured
to generate an output beam of 1 kW or greater at an output beam
wavelength; and one or more pump modules optically coupled via optical
splices to one or more pump or pump-signal fiber combiners optically
spliced to said gain module and configured to generate light at a pump
wavelength for optically pumping said gain module; wherein said gain
module is configured to receive pump light from said one or more pump
modules such that the power of the output beam is scalable in accordance
with the number and power of pump modules coupled via the optical splices
to the one or more pump or pump-signal fiber combiners optically spliced
to said gain module.

20. The system of claim 19 wherein the output beam is 2 kW or greater.

21. The system of claim 19 wherein each one of said one or more pump
modules comprises a plurality of laser diode modules optically coupled to
a pump module output fiber using one or more pump module pump combiners.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] Generally, the field of the present invention is high power fiber
lasers. More particularly, the present invention relates to scalable high
power continuous-wave and quasi-continuous-wave fiber lasers.

[0003] 2. Background

[0004] Conventional multi-kilowatt industrial fiber laser systems
typically employ a non-scalable architecture consisting of multiple
component fiber lasers whose outputs are combined with a fused-fiber
signal combiner. The total fiber laser system output power is typically
in the range of 2 to 6 kW, and the individual component fiber lasers
typically have a power in the range of 0.4 to 1.0 kW. Thus, in order to
reach total powers in excess of 1 kW, the outputs from multiple fiber
lasers (typically two to ten) must be combined.

[0005] Such conventional approaches for achieving a high power fiber laser
output have several drawbacks made apparent in light of the present
disclosure. For example, by combining the multiple individual fiber laser
systems significant redundancy is required in optical, electrical, and
mechanical components, thereby increasing the system cost, size, and
complexity. In addition, fiber laser component systems generally have
limited field serviceability, often requiring replacement of the entire
fiber laser component system if an optical component thereof fails. Such
entire replacement occurs even when the optical component failure is
localized to only a portion of the fiber component system, such as a
broken fiber. Requiring the replacement of entire fiber laser component
systems increases cost for repair of the complete multi-kilowatt system.
Field replacement of a fiber laser component system typically requires
highly specialized equipment and clean-room conditions, which are not
readily available in factory environments, making service costly and
disruptive.

[0006] The fused-fiber signal combiner causes optical loss and diminishes
the beam quality of the individual fiber laser outputs received. This
loss negatively impacts efficiency, which determines power consumption
and waste-heat generation, and beam quality degradation can reduce the
speed in metal-cutting applications. Furthermore, the signal combiner is
expensive, requiring costly equipment and considerable process
development and control for fabrication, and it can experience
unpredictable variation impacting reproducibility and reliability.
Fused-fiber signal combiners are also subject to operational damage,
including from optical feedback from the work piece, thereby decreasing
system reliability.

[0007] Utilizing a signal combiner to achieve up to a few kilowatts of
power also limits the ability for laser power of the fiber laser system
to be upgraded in the field. For example, a fused signal combiner may
include empty ports for receiving additional component fiber lasers.
However, the beam quality of output beam is degraded whether or not the
extra ports are populated with additional component fiber laser system
outputs. Also, if the signal combiner has fully populated input ports,
upgrading system output power requires the replacement of one or more of
the component fiber lasers with a component fiber laser of higher power.
Replacing component fiber lasers is expensive, particularly since there
is attendant with it limited or no re-use of the replaced component fiber
laser, subsystems, or components.

[0008] Conventional system designs are also limited with respect to how
technological advances can be accommodated or incorporated since many key
components are integrated into each component fiber laser. For example,
pump diode technology is advancing rapidly, providing increased power,
brightness, and efficiency and reduced cost. Active fibers have also
experienced significant technological gains in recent years.
Incorporating these advances into an existing fiber laser can be
difficult or impossible if the pump diodes, fibers, and electronics are
all integrated into a single laser module. For example, the
interconnections among components within a single laser module would
likely be inaccessible or not easily changeable, and changes to critical
components would entail significant design ripple, requiring
corresponding changes in the other components. Similarly, the mechanical
or thermal designs could be impacted by changing a critical component.
Thus, conventional high power fiber laser architectures often must either
forgo upgrades based on technological advances or commit to costly and
time consuming redesign.

[0009] A need therefore exists for a multi-kilowatt fiber laser
architecture that minimizes cost by eliminating component redundancy,
minimizes or eliminates the drawbacks of signal combiners, is easily and
cost-effectively serviceable in the field, enables field upgradability,
and is sufficiently flexible to accommodate technological advances
without significant cost or design ripple.

SUMMARY OF THE INVENTION

[0010] According to one aspect of the present invention, a modular and
scalable high power fiber laser system configurable to generate 1 kW or
more of laser output includes one or more separable pump modules
separately disposed from each other, each pump module including a
plurality of fiber-coupled component pump sources optically combined by
one or more fiber-based pump module pump combiners, each pump module
providing one or more pump module fiber outputs, and a gain module
separately disposed from the one or more separable pump modules and
including one or more gain module pump fiber inputs optically coupled to
corresponding ones of the pump module fiber outputs, and including a gain
fiber optically coupled to the one or more gain module pump fiber inputs,
the gain fiber configured to generate a gain module fiber output power
scalable in relation to the number and power of the pump module fiber
outputs coupled to the gain fiber.

[0011] According to another aspect of the present invention, a high-power
fiber laser system includes a gain module configured to generate an
output beam of 1 kW or greater at an output beam wavelength, and one or
more pump modules optically coupled to the gain module and configured to
generate light at a pump wavelength for optically pumping the gain
module, wherein the gain module is configured to receive pump light from
the one or more pump modules such that the power of the output beam is
scalable in accordance with the number and power of pump modules coupled
to the gain module.

[0012] The foregoing and other objects, features, and advantages will
become apparent from the following detailed description, which proceeds
with reference to the accompanying figures which are not necessarily to
scale.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1A is a perspective view of a fiber laser system in accordance
with an aspect of the present invention.

[0014] FIG. 1B is a connectivity diagram of the fiber laser system
depicted in FIG. 1A in accordance with an aspect of the present
invention.

[0015] FIG. 2 is a plan view schematic of a fiber laser system in
accordance with an aspect of the present invention.

[0016] FIG. 3A is a schematic of a pump module of a fiber laser system in
accordance with an aspect of the present invention.

[0017] FIG. 3B is a schematic of a pump module of a fiber laser system in
accordance with an aspect of the present invention.

[0018] FIG. 4 is a schematic of another pump module of a fiber laser
system in accordance with an aspect of the present invention.

[0019] FIG. 5 is a schematic of another pump module of a fiber laser
system in accordance with an aspect of the present invention.

[0020] FIG. 6 is a schematic of a gain module of a fiber laser system in
accordance with an aspect of the present invention.

[0021] FIG. 7 is a schematic of another gain module of a fiber laser
system in accordance with an aspect of the present invention.

[0022] FIG. 8 is a schematic of another gain module of a fiber laser
system in accordance with an aspect of the present invention.

[0023] FIG. 9 is a schematic of another gain module of a fiber laser
system in accordance with an aspect of the present invention.

[0024] FIG. 10 is a schematic of another gain module of a fiber laser
system in accordance with an aspect of the present invention.

[0025] FIG. 11 is a rear view of a gain module combiner of a fiber laser
system in accordance with an aspect of the present invention.

[0026] FIG. 12 is a rear view of another gain module combiner of a fiber
laser system in accordance with an aspect of the present invention.

[0027] FIG. 13 is a schematic of another gain module of a fiber laser
system in accordance with an aspect of the present invention.

[0028] FIG. 14 is a schematic of a combiner stage in accordance with an
aspect of the present invention.

[0029] FIG. 15 is a schematic of another gain module of a fiber laser
system in accordance with an aspect of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0030] A perspective view of a first embodiment of a highly configurable,
modular, and scalable continuous-wave or quasi-continuous-wave high-power
fiber laser system 1000 is shown in FIG. 1A. The fiber laser system 1000
includes several bays 1001 which modularly receive different system
modules, including system pump modules 1002 and system gain modules 1003,
each which can be configured to be separable from the fiber laser system
1000. Additional modules, such as a control module 1004 or a power supply
module, also can be modularly disposed in relation to the other system
modules of the system 1000. The scalable multi-kilowatt fiber laser
system 1000 is depicted in an optional mobile configuration, with a
plurality of system modules disposed in a vertical rack arrangement
mounted atop a plurality of casters 1005 for convenient movement in an
industrial environment. Pump modules 1002 provide one or more pump module
fiber outputs 1006 which are optically coupled to one or more gain
modules 1003. Fiber laser system 1000 includes a system output 1007
providing about 1 kW or more of output power for various industrial
applications and which can be provided by the one or more gain modules
1003. Output power of the system can be scaled by adding additional pump
modules 1002 in available system bays 1001 or by upgrading installed pump
modules 1002 by swapping old with new.

[0031] The modularity and scalability of embodiments herein present
numerous manufacturing advantages. For example, many different power
levels can be selected without requiring significant redesign between the
selected power level configurations. A configuration with a single pump
module 1002 and a single gain module 1003 can provide a particular system
output power which can be upgraded by installing an additional pump
module 1002 (see pump module 1002 shown in dashed lines in FIG. 1) and
splicing the pump module output 1006 to the gain module 1003. Due to the
modularity, size and weight can be divided between pump and gain modules
such that a single person in the field or factory can carry, implement,
or service each pump and gain module of the system. This advantage can be
particularly significant as the power from a single fiber laser is
increased, which has been a consistent trend in the industry; this power
scaling trend can continue without resulting in prohibitively large or
heavy modules because the pump modules and gain modules do not have to be
housed in a single module. The form factor of the laser system can also
be configured to support different deployment scenarios. For example,
system modules can be mounted in a rack vertically as shown in FIG. 1,
horizontally, or in another orientation, or combination thereof. Modules
can be physically separated from each other to facilitate integration
into a desired space.

[0032] In FIG. 1B a schematic is shown for an embodiment of a system 1010
similar to that shown in perspective view in FIG. 1A. The system 1010
includes a plurality of pump modules 1011 providing pump energy to a gain
module 1012 which is configured to generate a laser system output 1013.
The system 1010 can include one or more expansion slots 1014 to provide
configuration changes to the system 1010, such as additional pump or gain
modules. A cooling system 1015 is coupled to the pump and gain modules to
provide thermal stability therein and to the system 1010 as a whole. The
system 1010 is controlled by a controller 1015 configured to monitor and
adjust outputs and other properties of the pump modules, gain modules and
cooling system.

[0033] Referring now to FIG. 2, an embodiment of a high power fiber laser
system 20 is shown, in accordance with another aspect of the present
invention. The fiber laser system 20 is highly configurable and modular
such that the system 20 can be manufactured ab initio for operation at a
pre-selected range of output powers, such as between 1 kW or less and
multiple KWs, and for upgrade to higher output powers or different
performance criteria. The fiber laser system 20 includes one or more
component pump modules 22 each separately disposed from the other and
modularly separable from the system 20. Each component pump module 22
provides one or more component pump module outputs 24. The fiber laser
system 20 also includes one or more gain modules 26 separately disposed
from each other and modularly separable from the system 20. The one or
more gain modules 26 are optically coupled to the one or more component
pump module outputs 24, such that a fiber laser system output beam 28 is
produced at a predetermined output power. In the example shown in FIG. 2,
a single gain module 26 provides the system output beam 28 by utilizing
the pump power of three pump modules 22 coupled to the gain module 26.
Slots for additional modularly separable pump modules 22 are shown with
spots 23 while corresponding additional pump module outputs for coupling
to the gain module 26 are shown with dashed lines 27.

[0034] Gain module 26 includes a gain fiber incorporated into a laser
oscillator 30 providing laser oscillation between opposite fiber Bragg
gratings 31. In some examples, the gain fiber of the gain module 26
includes optical fiber sized to accommodate a predetermined highest
output power for the fiber laser system 20. For example, in some
embodiments selected maximum operating output powers are in the kW range,
such as 1 kW, 2 kW, 3 kW, 4 kW, 5 kW, or higher. The maximum output power
of the fiber laser system 20 is determined by the number and output power
of pump modules 22 capable of being spliced to the gain module 26. Thus,
the fiber laser output beam 28 can be produced without using a plurality
of redundant oscillator or amplifier systems, without redundant
supporting mechanical and electrical components, and without using a
signal combiner to combine a plurality of redundant component fiber laser
outputs.

[0035] The separate and modular nature of the pump and gain modules 22, 26
allows each to be serviced separately. For example, if a fiber failure
occurs in the gain module 26, the gain module 26 can be replaced while
each of the installed pump modules remains intact without any or
substantial modification. Similarly, if a pump module 22 fails in some
fashion, the pump module 22 can be replaced, leaving each other pump
module 22 and the gain module 26 in place without any or substantial
modification thereof. Systems herein provide robustness advantages as
potential failures are more likely to be isolated to particular system
modules, which can be interchanged and upgraded without replacing an
entire system.

[0036] In preferred examples, a pump module 22 includes one or more
semiconductor diode laser modules 34 each including one or more
semiconductor diode lasers providing one or more diode laser output beams
combined and coupled to a diode laser module output optical fiber 36. A
plurality of output optical fibers 36 are optically coupled to a pump
module pump combiner 38 to combine the diode laser module pump light into
a pump module output 24. Pump module pump combiners 38 are configured to
transmit low-brightness multimode pump light in a large core, as opposed
to signal combiners, which transmit high-brightness signal light in a
small core. Pump combiners are often manufactured at less cost than
signal combiners since the performance requirements, such as beam quality
at the combiner output and optical insertion loss, are typically less
demanding.

[0037] Combined pump light is coupled out of the pump module 22 through
one or more pump module outputs 24. The pump module outputs 24 are
optically coupled (e.g., by fiber splicing) to the gain module 26 onto a
fiber combiner 40 thereof. The fiber combiner 40 can be the similar in
design to the pump module pump combiner 38 associated with each pump
module 22. However, in preferred examples, the combiner in the gain
module can be a pump-signal combiner, which transmits both signal and
pump light. As will be described further hereinafter, pump-signal
combiners can be used at a back end of the gain module gain fiber, at a
front end of the gain fiber to launch counter-propagating pump light,
within or between gain stages (e.g., between an oscillator and an
amplifier or between amplifiers), or some combination thereof. In various
examples herein, since the performance requirements of the fiber splices
between the pump and gain modules are often lower than those for splices
that must transmit signal light (e.g., between a component fiber laser
and a signal combiner in conventional designs), splicing requirements are
relaxed concomitantly, allowing for in situ splicing of the pump module
outputs 24 to selected gain module inputs of the fiber combiner 40 under
less than clean-room conditions using commercially available equipment.
Alignment sensitivity and cleave-angle requirements are lower for
splicing outputs 24 to fiber combiner 40 as compared to the splicing of
fibers to signal combiners, also contributing to the accessibility of
splicing fibers to the fiber combiner 40 in a factory or other field
environment. For glass-clad fibers, splicing of the pump module outputs
24 to the fiber combiner 40 is insensitive to contamination and
consequently suitable for use in field and factory environments. In some
examples, pump module outputs 24 are coupled to gain module 26 via
connectors pluggable into the pump module or the gain module or both,
eliminating the need for splicing and further enhancing modularity of the
fiber laser system.

[0038] In addition to enhancing the field serviceability of the fiber
laser system 20, the modular separation of the pump modules and gain
module allows for field upgradability of the system 20 to higher
allowable output powers. For example, additional pump modules 22 can be
spliced to open pump fiber inputs of the fiber combiner 40 of the gain
module. Additional pump modules 22 can be identical to or different from
existing modules 22 spliced to the gain module 26 such that laser output
28 of the system 20 can be selectably scaled to higher powers. Similar to
servicing an existing system 20, the procedure for splicing the pump
module outputs 24 of the additional pump modules 22 to the fiber inputs
of the fiber combiner 40 is relatively simple and can be performed in a
factory or other field environment. The modular separation between pump
modules and gain module also allows for scalable power output of the
system 20 because the physical separation between pump modules and
between the gain module and pump modules reduces or eliminates thermal
crosstalk between modules. Each module can be provided with independent
water-cooling ports such that modules can be cooled separately or cooled
together in parallel or in series. In one example high power fiber laser
system built in accordance with aspects of the present invention a 3 kW
fiber laser output power can be generated with three 1.5 kW pump modules
being spliced to the gain module. In another example, building or
upgrading the fiber laser system to have three 2.0 kW pump modules can
provide a 4 kW fiber laser output power. In some examples, one or more
backup pump modules can be provided in the fiber laser system 20 for use
in the event of the failure of another pump module. The system 20 can be
configured to switch over to the backup pump modules immediately upon
failure, or slowly as one or more other active pump modules degrade over
a period of time. The separable nature of the pump modules further allows
for failed modules to be replaced in situ with new pump modules without
affecting the operation of the backup pump modules or fiber laser system.

[0039] In addition to field serviceability and field power expandability,
the modularity of system 20 provides for adaptability to various
technology improvements, ensuring compatibility of the system 20 and its
existing modules with the pace of innovation in the laser industry. For
example, improvements in pump diode technology could provide for an
upgraded pump module 22. The upgraded pump module can be substituted for
an existing pump module 22 or can be used in addition to existing pump
modules 22, providing improved system performance, efficiency, cost, or
any combination thereof, without requiring significant design changes or
replacement of components that have not been upgraded. Similarly,
improvements in gain module technology such as oscillator or amplifier
architecture might provide for an upgraded gain module 26. The upgraded
gain module can be substituted for the existing gain module 26 without
requiring replacement or modification of the pump modules. The various
substitutions can again be performed in the field or factory environment.

[0040] In many industrial applications for kW fiber lasers, single-mode
output beam quality is not required. Accordingly, conventional
architectures typically combine the outputs of fiber lasers producing
single-mode signal beams using a signal combiner to produce a multimode
output beam. In some examples of fiber laser system 20, the gain module
26 does not produce single-mode output since such output is not required
for many applications. Because the desired output is multimode, systems
20 can achieve such output without the need for the complexity of
single-mode combination. Also, because single-mode operation of the gain
module 26 is not required, the ability to scale the power of the gain
module 26 to multiple kW outputs is more accessible. Allowing the gain
fiber of the gain module 26 to be multimode facilitates power scaling in
a more practical manner than by maximizing the single-mode output power
of an individual fiber laser since the single-mode power limit is lower
than the multimode power limit. Single-mode fiber lasers are typically
limited to a power level of around 1-2 kW, resulting in the requirement
that multiple fiber lasers be combined in order to reach multiple kW
power levels; approaches to scaling the single-mode power beyond this
level typically entail cost, complexity, and/or inefficiency that are
undesirable for an industrial laser system.

[0041] In other embodiments, a single-mode system output may be desirable,
and gain module 26 can be configured for single-mode output. A
single-mode gain module 26 is typically rated at a lower output power
than counterpart systems with multimode outputs. However, the modularity
of the architecture of the system 20 allows a multimode gain module to be
swapped with a single-mode gain module. In one example, a single-mode
gain module can be rated for an output of 1 kW while a multi-mode gain
module can be rated for an output of 3 or 4 kW.

[0042] In typical examples of gain module 26, beam quality of the output
beam 28 is generally dependent upon the maximum power rating of the gain
module such that higher power ratings for gain module 26 generally
correspond with a lower beam quality for output beam 28. Some particular
examples of gain modules 26 can be rated at a maximum power rating higher
than other particular examples of gain modules 26, and for the same
output level the higher rated module will provide an output beam 28 of
lower beam quality than the output beam 28 with the lower power rated
module. However, in fiber laser system examples herein that do not
utilize fused signal combiners such that undesirable beam quality
degradation in the output beam 28 is correspondingly avoided, a higher
power rated gain module 26, configured to receive multiple pump module
outputs 24, is made possible. Thus, provision for receiving a plurality
of pump module outputs 24 in the gain module 26 does not represent a
significant beam quality compromise for system 20 configured for multiple
kW power output and may provide better beam quality than a system with
similar output power based on combining the outputs of single-mode fiber
lasers.

[0043] Conventional kW fiber laser systems for industrial materials
processing applications typically provide a beam parameter product (BPP,
a standard measure of beam quality) of 2.3-3.0 mm-mrad at a power level
of 2-4 kW, and the BPP is generally larger (i.e., worse beam quality) at
higher powers. By eliminating the signal combiner according to various
aspects of the present invention, an output with a higher beam quality is
possible. For example, with presently available pump diodes, a beam
quality of less than about 1 mm-mrad is possible at 2 to 3 kW and less
than about 2 mm-mrad is possible at 4 to 5 kW.

[0044] Modular pump modules can be provided in a variety of selectable
configurations. With reference to FIG. 3A, a pump module 42 is shown that
includes a plurality of semiconductor diode laser modules 44. Diode laser
modules 44 are fiber-coupled such that the diode laser light generated in
the laser module 44 is directed into an output optical fiber 46. The
plurality of output optical fibers 46 are combined with a fused-fiber
pump combiner 48. Combiners are typically made of glass and are tapered
or fused to collapse multiple optical fiber inputs to fewer or one
optical fiber output. The light coupled into the combiner 48 is combined
and directed into a pump module output 50. Different types of diode laser
modules 44 may be used, which can provide different levels of laser beam
brightness or irradiance, as well as power output. Consequently, in some
examples, fewer of a particular type, more of a particular type, or
different types of diode laser modules 44 may be used to achieve the same
desired power output of the pump module 42. With combiner 48 the
plurality of output optical fibers 46 is combined in a single stage to
provide a pump module output 50, which can be polymer-clad or glass-clad
or both, for subsequent optical coupling to a gain module (not shown). In
FIG. 3B, a pump module 43 is shown that includes a single semiconductor
diode laser module 45. Diode laser module 45 provides a sufficient amount
of optical pumping power for coupling into a pump module output 50
without requiring the use of a pump combiner to combine multiple diode
laser modules in the pump module.

[0045] Referring to FIG. 4, another example is shown for a pump module 52
employing a plurality of diode laser modules 54 in a multi-stage combiner
configuration. The diode modules provide fiber-coupled outputs 56 which
are combined with first-stage pump fiber combiners 58. The combiners 58
provide first-stage combiner outputs 60 which are then coupled in a
second-stage pump combiner 62. Second-stage pump combiner 62 may be the
same or similar to first-stage combiner 58 depending on the brightness,
power, or other requirements and characteristics of the multi-stage pump
module 52. The light coupled into the second-stage combiner 62 is
combined and provided as a pump module output 64, which can be
polymer-clad or glass-clad or both, for subsequent optical coupling to a
gain module (not shown).

[0046] In FIG. 5 another embodiment of a pump module 66 is shown providing
a plurality of pump module outputs. Pump module 66 includes a plurality
of diode laser modules 68 providing laser pump light to respective
fiber-coupled output optical fibers 70. A first set of output optical
fibers 72 is coupled into a first pump combiner 74. The pump light is
combined with the pump combiner 74 and directed to a glass-clad or
polymer-clad (or both) first pump module output 76. A second set of
output optical fibers 78 is coupled into a second pump combiner 80. The
second combiner 80 combines the received pump light and directs the light
to a second glass-clad or polymer-clad (or both) pump module output 82.
In other embodiments, pump module 66 has more than two pump module
outputs. As shown, pump outputs 76, 82 include pluggable connectors 83 at
a boundary of the pump module 66. Connectors 83 can facilitate the
modularity of the pump modules herein by allowing separate patch cables
to be used to connect pump modules and gain modules or by simplifying
connection between pump modules and gain modules. However, optical
splices can also be used to connect outputs of pump module 66 to gain
modules herein.

[0047] In FIG. 6 an alternative embodiment of a gain module 84 is shown.
Gain module 84 includes a plurality of polymer-clad, glass-clad, or both
glass and polymer-clad pump inputs 86 which may be received from or may
be the same as pump module outputs (not shown). As shown, pump inputs 86
are coupled into the gain module 84 via pluggable connectors 87, though
optical splices may also be used. The pump inputs 86 are optically
coupled to a gain module fused pump or pump-signal combiner 88 which
combines received pump light and couples the light into gain module
combiner output 90. The combined pump light of the combiner output 90 is
coupled or spliced into a fiber laser oscillator 94 which converts
incident pump power to a gain module output 96. The gain module output 96
can be used as a system output or it can be combined further with an
additional module. The fiber laser oscillator 94 generally includes an
optical gain fiber 98 in which the pump light is coupled and in which the
gain module output 96 is generated, a high reflector 100 configured to
reflect the laser energy to produce the output 96 and to transmit
incoming pump light, and a partial reflector 102 configured to transmit
at least a portion of the laser energy for output 96. The high and
partial reflectors can be fiber Bragg gratings or other suitable
reflective optical components.

[0048] In FIG. 7 another alternative embodiment of a gain module 104 is
shown for a master oscillator power amplifier (MOPA) configuration. Gain
module 104 includes a plurality of polymer-clad and/or glass-clad pump
inputs 106 coupled to a gain module fused pump-signal or pump combiner
108. The combiner 108 receives pump light through the pump inputs 106 and
combines and couples the beams into a combiner output fiber portion 110.
The combined pump light of the combiner output 110 is coupled or spliced
into a fiber laser oscillator 112 which converts a first portion of
incident pump energy to signal energy for gain module output 116. The
fiber laser oscillator 112 can include an optical gain fiber 114 in which
the pump light is coupled and in which the signal energy of the gain
module output 116 is generated, a high reflector 118 configured to
reflect signal energy and to transmit incoming pump energy, and a partial
reflector 120 configured to transmit at least a percentage of the signal
energy. A first amplifier 124 receives the signal light and amplifies the
power thereof with pump light energy. In other embodiments, one or more
additional amplifiers can be added in sequence after first amplifier 124
to vary the maximum power rating and beam quality of the gain module
output 116.

[0049] In another embodiment of a gain module 144, shown in FIG. 9, the
output fibers 146 from one or more pump modules are coupled into a gain
fiber 148 using one or more pump-signal combiners 150 at one or more
positions along the gain fiber 148 to provide side-pumping therein in
order to produce a gain module signal output 152. The one or more
pump-signal combiners 150 can be used in connection with gain fiber 148
in an oscillator configuration, such as the oscillator shown in FIG. 6,
or a MOPA configuration as shown in FIG. 7. The combiners 150 can be used
to couple light into the gain fiber 148 at various positions, including
between the high reflector and the oscillator fiber, between the
oscillator and amplifier fibers, between amplification stages, or some
combination thereof. Moreover, pump light can be launched in the
direction of the signal beam in a co-propagating manner, in the direction
opposite the signal beam, i.e., in a counter-propagating manner, or both.
In some examples providing side-pumping, a plurality of gain fibers 148
are disposed in the gain module in parallel so as to produce more than
one gain module output 152. Similarly, it will be appreciated that for
other various gain module embodiments herein a plurality of gain fibers
can also be disposed therein in parallel so as to produce a plurality of
gain module outputs.

[0050] In another embodiment of a gain module 154, shown in FIG. 10, an
oscillator 156 is bi-directionally pumped to produce a gain module output
158. Pump light from one or more pump modules is launched via gain module
input fibers 160 in the co-propagating direction using a combiner 158
such as a pump or pump-signal type before a high reflector 162 of the
oscillator or a combiner 159 such as a pump-signal type between the high
reflector 162 and the oscillator. In addition, pump light from one or
more pump modules is launched in the counter-propagating direction using
a pump-signal combiner 164 such as between the oscillator and a partial
reflector 166 thereof or after the partial reflector.

[0051] In FIG. 8 there is shown an embodiment of a gain module 126 that
includes a plurality of polymer-clad and/or glass-clad pump inputs 128, a
gain module combiner 130 optically coupled to the inputs 128 so as to
receive the pump light therefrom, and one or more gain fiber gain stages
132, such as oscillator and amplifier stages, coupled to the gain module
combiner 130. The gain stages 132 receive the pump light and are operable
to generate and amplify a signal beam to be provided at an output 136 of
the gain module 126. As shown, an even or odd number of pump inputs 128
(in this case an even number of six inputs forming a 7×1 combiner)
are coupled to the inputs 138 of the gain module combiner 130. A central
polymer-clad and/or glass-clad input 140 is coupled to the combiner input
138. The central input 140 is optically coupled to an aiming laser 142,
which directs a beam through the combiner 130, gain stages 132, and
output 136 to provide an aiming beam that can be used to indicate the
direction of a beam emitted from the output 136 of the gain module; the
aiming beam is typically visible to the unaided eye, such as a red or a
green wavelength.

[0052] FIGS. 11 and 12 illustrate example arrangements of pump inputs
received by various gain modules and coupled to combiners therein. FIG.
11 shows the arrangement on the combiner depicted in FIG. 8 where an even
number of six pump inputs 128 are coupled to the input 138 around a
central input 140 which can be an aiming laser input or another pump
input. In FIG. 12 an arrangement of nineteen inputs 168 is shown,
including a central input 170, coupled to a combiner 172. The central
input 170 can be used for pumping or an aiming beam. In other examples,
such as pump-signal combiner examples described herein, the central
inputs can be dedicated to signal propagation. In various combiner
examples herein, unused gain module combiner inputs can be paired and
conveniently spliced together in the gain module for storage and future
use and splicing of additional pump modules or after removal of pump
modules. The spliced inputs can also recirculate pump light and signal
light back through the gain module, potentially increasing gain module
efficiency. Through recirculation, light that should otherwise be managed
and heat sunk at the termination of the unused pump input can be
redirected to designed heat sinking locations, for example, via one or
more cladding light strippers, where supporting thermo-mechanical systems
are configured to handle and remove the heat load.

[0053] In FIG. 13 another exemplary embodiment of a gain module 180 is
shown that includes a plurality of pump inputs 182, a gain module
combiner 184 optically coupled to the inputs 182, and one or more gain
stages 186 coupled to the gain module combiner 184 and which produce a
gain module output 188. A central polymer-clad and/or glass-clad fiber
input 190 is coupled to a central location of an input 192 of the
combiner. An aiming laser 194 is coupled to the central pump input 190
directly or with a beam-splitter 196. A beam dump 198 is also coupled to
the central pump input 190 and is configured to receive, monitor, and
heat sink or otherwise dispose of undesirable backward-propagating light
from the gain module gain fiber. For example, light reflected at a target
can become back-coupled into the gain module 180 through the output 188
thereof and cause damage to the one or more gain stages 186 or other
components such as upstream pump modules.

[0054] Thus, it will be appreciated that some examples herein provide
particular advantages over conventional approaches to configuring high
power continuous-wave or quasi-continuous-wave fiber lasers in industrial
settings. Herein, fiber laser power levels of 1 kW or more are achievable
in a scalable and modular way such that multiple kilowatt output power
can be selectably obtained. Pump sources become separated from the gain
fiber and corresponding gain stages, improving serviceability,
manufacturability, and field upgradeability and to take advantage of
future advances in various component technologies. Variable pump module
populations and ease of adjusting population enhances system flexibility
and upgradeability in system output power.

[0055] In further examples, with reference FIG. 14, a gain module 200 and
a combining module 202 are shown. The gain module includes two or more
sets of pump inputs 204, each set coupled to a corresponding gain module
combiner 206, and each combiner coupled to a corresponding one or more
gain fiber gain stages 208. The separate sets of components can be
configured to produce a plurality of gain module outputs 210 each with kW
to multi-kW output levels. The separate multiple gain module outputs 210
can be used for various direct applications, or they can be coupled to
combining module 202. The combining module utilizes a signal combiner 212
that can be modularized to be separate from gain module 200 or the signal
combiner 212 thereof can be included instead as part of the gain module
200. The internal or external signal combiner 212 can be used to combine
the various single-mode or multimode outputs 210 from the gain module 200
to produce a combined fiber output 214 capable of providing a very high
power output beam in the multiple kW regime. For example, average power
outputs of 4 kW, 6 kW, 8 kW, 10 kW, 12 kW or even higher can be achieved.
In additional examples, separate gain modules can provide single gain
module outputs that can be combined in combining stage 202 internal or
external to gain module 200.

[0056] In further examples, with reference to FIG. 15, a gain module 220
is shown that includes a pair of gain fibers 222 end-pumped by a
plurality of pump inputs 224 coupled to the respective gain fibers 222
with combiners 226. High-power multimode or single-mode gain fiber
outputs 228 are coupled into a signal combiner 230 that combines the
high-power gain fiber outputs 228 into a single high-power output 232 of
the gain module 220. In one example, gain fiber outputs provides optical
powers of 4 kW respectively that are combined with the signal combiner
230 to provide a gain module output of about 8 kW. It will be appreciated
that various output powers or ranges of output powers can be provided for
gain module 220 by varying the number and type of scalable pump modules
and pump inputs thereof coupled to the gain module 220 and also by
varying the architecture of the gain module in accordance with the
various embodiments and teachings herein. It is thought that the present
invention and many of the attendant advantages thereof will be understood
from the foregoing description, and it will be apparent that various
changes may be made in the parts thereof without departing from the
spirit and scope of the invention or sacrificing all of its material
advantages, the forms hereinbefore described being merely exemplary
embodiments thereof.